Reducing fouling deposits in process equipment

ABSTRACT

TO REDUCE OR PREVENT THE FOULING OF PROCESS EQUIPMENT IN PETROLEUM OR CHEMICAL INDUSTRIES WHEREIN AN ORGANIC FEEDSTOCK IS SUBJECTED TO HEAT EXCHANGE AT A TEMPERATURE OF FROM ABOUT 200* TO ABOUT 1300*F., GHERE IS ADDED TO THAT ORGANIC FEEDSTOCK A VERY LOW CONCENTRATION, OF THE ORDER OF ABOUT 0.5 TO 200 PARTS PER MILLION, A MIXTURE OF ABOUT 75 TO 99 ST. PERCENT OF A FATTY ACID ESTER OF AN ALKANOLAMINE AND FROM ABOUT 1 TO 25 WT. PERCENT OF A PHOSPHOROUS ACID OR A MONO, DI, OR TRI-ORGANIC PHOSPHITE ESTER HAVING THE FORMULA:   R-O-P(-O-R&#39;&#39;)-O-R&#34;   WHEREIN R, R&#39;&#39; AND R&#34; ARE HYDROGEN OR A HYDROCARBON RADICAL, INCLUDING ALKYL, ARYL, ARALKYL, ALKARYL, CYCLOALKYL, OR ALKENYL, OR A SIMPLE HALOGENATED DERIVATIVE OF SUCH HYDROCARBON RADICAL.

United States Patent Ofice 3,645,886 REDUCING FOULING DEPOSITS INPROCESS EQUIPMENT Bruce G. Gillespie, Cranford, and Jack E. Ryer, EastBrunswick, N.J., assignors to Esso Research and Engineering Company NoDrawing. Continuation-impart of application Ser. No. 778,751, Nov. 25,1968, now Patent No. 3,558,470, which is a continuation-in-part ofapplication Ser. No. 694,039, Dec. 28, 1967. This application May 15,1970, Ser. No. 37,846

Int. Cl. Cg 9/16; C101 1/26; C23f 14/00 US. Cl. 208-48 AA 9 ClaimsABSTRACT OF THE DISCLOSURE To reduce or prevent the fouling of processequipment in petroleum or chemical industries wherein an organicfeedstock is subjected to heat exchange at a temperature of from about200 to about 1300 F., there is added to that organic feedstock a verylow concentration, of the order of about 0.5 to 200 parts per million, amixture of about 75 to 99 wt. percent of a fatty acid ester of analkanolamine and from about 1 to 25 wt. percent of a phosphorous acid ora mono, di, or tri-organic phosphite ester having the formula:

wherein R, R and R" are hydrogen or a hydrocarbon radical, includingalkyl, aryl, aralkyl, alkaryl, cycloalkyl, or alkenyl, or a simplehalogenated derivative of such hydrocarbon radical.

This application is a continuation-in-part of copending application Ser.No. 778,751, filed Nov. 25, 1968 (now US. Pat. 3,558,470), which in turnis a continuation-inpart of application Ser. No. 694,039, filed Dec. 28,1967, and now abandoned.

This invention concerns a method for reducing or preventing the foulingof process equipment in chemical industries. It is particularlyapplicable to process equipment involving heat transfer at hightemperatures. Preferably, the improved method comprises adding to thefeedstock of a processing unit handling a hydrocarbon fraction or otherorganic chemical stream being heated, a very low concentration of amixture of a fatty acid ester of an alkanolamine and a phosphite esteror a phosphorous acid.

In industrial processes that involve the heating of a feedstock to ahigh temperature, particularly in the petroleum industry, severe foulingof the equipment is often encountered. This is particularly so in thedistillation of crude oils, in naphtha desulfurization processes, in gasoil cracking units, and in visbreaking operatings involving heavypetroleum fractions. Thus, fouling problems may occur when feedstocksare heated to any temperature Within the range of from about 220 F. upto cracking temperatures, and particularly at temperatures of 200 to1300 F. The fouling problem is a serious one because, among otherthings, it causes heat transfer losses, increased pressure drops, andloss in throughput. The types of mechanical equipment that are mostfrequently affected by fouling include furnaces, pipes, heat exchangers,reboilers and condensers.

The deposits that are encountered as a result of the fouling phenomenonmay consist of sticky, tarry, polymeric, or carbonaceous material. Insome instances the fouling deposits will be associated with inorganicma- 3,045,886 Patented Feb. 29, 1972 terials such as sand, scale, orsalts which are cemented or otherwise caused to adhere to the surface ofthe equipment by this type of sticky, tarry, or carbonaceous foulingmaterial. The sand may be present because of the lack of properfiltering of the crude oil that is being fed to the unit, while thescale may occur from deterioration of the metal in the equipment. Saltsoccur in the crude oil stream as a result of incomplete desalting of thecrude or because the crude has not been subjected to any desaltingtreatment. Ordinarily, a crude is not desalted if the amount of saltdoes not exceed about 20 pounds per 1000 barrels of oil.

The fouling problems that are solved by the present invention are notconfined solely to those wherein inorganic salts or sand or scale arealso present, but include any of the fouling phenomena encountered inhigh temperature processing. Such fouling is believed to involvepolymerization, or a combination of polymerization and oxidation oroxidative polymerization which in some respects is similar to that whichcauses gum to form in gasoline. The high temperatures that are attainedin a heat transfer operation such as in the distillation of a crude oilor in process heating equipment feeding a catalytic reforming operationor a visbreaking operation, for example, can cause oxygen to react withthe hydrocarbons in the feed to form a polymeric material which candeposit on the surfaces of the heat transfer equipment. If thispolymerization can be prevented, fouling will likewise be prevented,since the binder for the inorganic deposits will thereby be eliminated.While fouling sometimes can be controlled by excluding oxygen from thefeedstock, often this is not economically feasible. For example, theordinary floating roof tank in which feedstocks are frequently storedwill not completely prevent contact with oxygen of the air. Furthermore,many feedstocks contain oxygen when they are received at the refinery orat a unit in the refinery. When oxygen contamination thus cannot beprevented, use of an antifoulant is one solution to the problem.

DESCRIPTION OF THE PRIOR ART Various antifoulants have been suggested inthe prior art. For example, US. Pat. 3,235,484, and its Reissue 26,330,teach the use of acylated amines, e.g. imides, prepared from polyaminesand aliphatic substituted succinic acids or their anhydrides asantifoulants for hydrocarbon feedstocks that are subjected to hightemperatures. Also, US. Pat. 3,364,130 teaches the use of amidecondensation products of monocarboxylic acids and polyamine. ApplicationSer. No. 778,751, of which the present application is acontinuation-in-part, discloses and claims the use as an antifoulant ofa mixture of a phosphorus acid or of a mono-, dior tri-organo phosphiteester and an amide or imide condensation product of the types describedin the aforementioned patents.

DESCRIPTION OF THE INVENTION In accordance with the present invention ithas been found that an antifoulant that is superior to prior artantifoulants comprises a mixture of an alkanolamine ester of a saturatedor unsaturated fatty acid and a phosphorus acid or a phosphite ester.The phosphorous acid or the phosphite makes up from 1 to 25 wt. percent,or more usually 1 to 20 wt. percent, of the mixture, and thealkanolamine ester makes up from to 99%, or more usually to 99 wt.percent, of the mixture.

The alkanolamine ester is the reaction product of an alkanolaminewherein the alkanol group has from 2 to 5 carbon atoms and from 1 to 3alkanol groups, with' a saturated or unsaturated fatty acid having fromabout 12 to 24 carbon atoms. A particularly effective alkanolamine estercomprises an ethanolamine ester, particularly the ester ofdiethanolamine or triethanolamine with oleic acid or with a mixture offatty acids containing oleic acid. Other suitable fatty acids includelauric, myristic, linoleic, arachidic, palmitic, stearic, hypogaeic,eicosinic, elaidic, eleostearic, and punicic. Particularly suitable is amixture of fatty acids from tall oil.

Suitable alkanolamines, include ethanolamine, isobutanolamine,pentanolamine, diethanolamine, 2 amino-2- methylpropanol 1, methyldiethanolamine, 2-amino-2- methylbutanol l, triethanolamine, butylethanolamine, monoisopropanolarnine, diethyl ethanolamine,diisopropanolamine, triisopropanolamine, dimethyl isopropanolamine, anddibutyl isopropanolamine. A particularly useful mixture of alkanolaminescomprises the still bottoms from the distillation of triethanolamine.These bottoms are predominantly triethanolamine along with variousamounts of higher boiling compounds. See, for example, Kirk- OthmerEncyclopedia of Chemical Technology (Second Edition), vol. 1, page 814.Usually in preparing the esters, more than stoichiometric proportions ofalkanolamine to fatty acid will be used.

The phosphite ester or phosphorus acid additive em ployed in associationwith the alkanolamine ester will be either a mono-, a di-, or atri-ester, or mixtures of two or more of these three types of esters, ora phosphorus acid, or a mixture of phosphorus acid and one or morephosphite esters. The organic substituent employed in the esterformation, and which is generally obtained from the respectivemonohydric alcohol or phenol in a conventional manner, is a hydrocarbylor halogenated hydrocarbyl radical. The phosphorus acid or phosphite canbe represented by the formula:

wherein R, R and R" are hydrogen or a hydrocarbyl radical selected fromthe group consisting of alkyl, haloalkyl, aryl, haloaryl, alkaryl,haloalkaryl, cycloalkyl, halocyclo alkyl, alkenyl, haloalkenyl, aralkyland haloaralkyl.

The total number of carbon atoms for each of R, R' and R" ranges betweenabout 1 and about 50 with the preferred range being between about 8 andabout 20 carbon atoms per hydrocarbyl radical. Typical examples of thephosphite esters and phosphorus acid are the following specificphosphite compounds (the specific listing of the monoester is intendedto include the like listing of the corresponding diand tri-ester aswell; thus, for example, methyl phosphite is intended to includedimethyl phosphite and trimethyl phosphite, but in instances where R, R'and R" are not the same, the diand tri-esters are set forth in full).The examples include: phosphorus acid; methyl phosphite; ethylphosphite; n-propyl phosphite; isopropyl phosphite; butyl phosphite;pentyl phosphite; hexyl phosphite; cyclohexyl phosphite; heptylphosphite; nonyl phosphite; decyl phosphite; lauryl phosphite; cetylphosphite; octadecyl phosphite; heptadecyl phosphite; phenyl phosphite;alpha or beta naphthyl phosphite; benzyl phosphite; tolyl phosphite;methyl, phenyl phosphite; dimethyl, phenyl phosphite; arnyl, phenylphosphite; bis(diamyl phenyl) phosphite; diamyl, phenyl phosphite;nonylphenyl phosphite; nonyl, phenyl phosphite; 4-amylpheny1 phosphite;4-amylphenyl, diethyl phosphite; dioctadecyl di-phenyl phosphite;octadecyl di-phenyl phosphite; isobutyl phenyl phosphite; nonyltolylphosphite; nonyl, ditolyl phosphite; polyisobutenyl diphenyl phosphite;dipolyisobutenyl phosphite; di-polyisobutenylphenyl phosphite;polyisobutenylphenyl phosphite; bromoethyl phosphite; chlorobutylphosphite; chlorooctyl phosphite; fluorophenyl phosphite; chlorobenzylphosphite; chlorotolyl phosphite; bromopolyisobutenyl, diphenylphosphite; di- (chloropolyisobutenyl) ethyl phosphite;di-polyisobutenyl, chlorobenzyl phosphite; di-polyisobutenyl,chloropolyisobutenyl phosphite. Particularly useful are the diesters andtriesters of C to C monoalkyl and dialkyl phenols, e.g.

of diamyl phenol, hexyl phenol, isooctyl phenyl, nonyl phenol, dodecylphenol, and hexadecyl phenol. Nonyl phenol made commercially byalkylation of phenol with tripropylene usually is a mixture of a majorproportion of monononyl phenol with a minor proportion of dinonylphenol.

Many of the above esters, particularly those containing the smallernumber of carbon atoms per molecule, are readily available commerciallyand their methods of preparation are conventional. Some of the esters,particularly those having the longer alkyl chains or hydrocarbonradicals or halogenated hydrocarbon radicals of the higher number ofcarbon atoms per radical, although presently not available commercially,are readily prepared by reaction one, two, or three moles of thecorresponding a1- cohol or phenol with each mole of phosphorus trihalidesuch as phosphorus trichloride or phosphorus tribromide. This is aconventional reaction and while there are other ways, also conventional,of producing these various phosphite esters, the present invention isnot concerned with the particular method by which the phosphite estersare produced. In those cases where monoor di-esters are formed, it issometimes desirable, following the esterification reaction, to treat thereacted mixture with water, dilute aqueous caustic, or dilute aqueousmineral acid in order to hydrolyze off the residual chlorine or bromineatoms present by reason of the particular trivalent phosphorus compoundemployed as an original reactant. The hydrolysis of a phosphorustrihalide yields phosphorous acid also.

The invention is particularly applicable to the treatment of anynormally liquid hydrocarbon feed stream and especially to the treatmentof liquid petroleum fractions ranging through light distillate stocks,e.g., naphthas, kcrosenes and the like, middle distillate stocks such asgas oils, lubricating oil fractions, cycle stocks from crackingoperation, virgin crude oils, topped crude oils, etc., as well asindividual hydrocarbon streams, as for example ethyl benzene ordicyclopentadiene.

The invention can be applied to any of a number of treating steps,including treating a crude petroleum feedstock entering a crudedistillation unit, the reduced crude feedstock entering a visbreakingunit, the light naphtha stock entering a pre-treating zone prior to acatalytic reforming zone, the naphtha or heavier feedstock entering thefeed heat exchanger to a desulfurizing unit, and the gas oil feedentering the preheater of a catalytic cracking unit. Other processes towhich the method is applicable include thermal hydrodealkylation ofaromatics, dehydrogenation of ethyl benzene, high temperature steamcracking or petroleum hydrocarbons, and depolymerization ofdicyclopentadiene. While the antifoulant could be fed directly to theunit in which fouling occurs, it is preferred to add it to the feedstockjust ahead of the zone in which the problem arises.

Only relatively small amounts of the alkanolamine ester containing theadded phosphite ester or phosphorous acid are required in order toproduce outstanding results in the reduction of fouling deposits. Ingeneral, the combined amount of the dual additive will range from about0.5 to about 200 parts per million (ppm) by weight based on the totalfeedstock. While amounts greater than 200 ppm. can be employed, usuallythis is not eco nomically justified because the possible increasedantifouling effect is not sufficiently great to warrant the use of largeamounts of the additive. Generally, in the treatment of the variouspetroleum feedstocks, the amount of the dual antifoulant will be fromabout 0.5 to 60 parts per million by weight. Some hydrocarbon streams,e.g. dicyclopentadiene, may require as much as ppm. of antifoulant. Theuse of the antifoulant does not interfere in any way with the process towhich the feed stream is being subjected.

In some instances reduction of fouling is further improved by employingin conjunction with the antifoulant additives certain antioxidants,including phenyl alphanaphthyl amine, and amino alkyl phenols, which arethe condensation products of C to C aldehydes, C to C alkylene diaminesand alkyl phenols of C to C alkyl groups. These antioxidant materialsmay comprise from 5 to 50% by weight of the antifoulant package.

Admixtures of the alkanolamine esters and the phosphite esters and/orphosphorous acid will normally be used as such. The invention alsoencompasses the reaction products of such alkanol-amine esters with thephosphite material (which includes phosphorous acid).

The following examples, which include a preferred embodiment, areintended to illustrate this invention. However, it is not intended thatthe invention be limited to these examples.

Example 1 Triethanolamine still bottoms, weighing 9.4 pounds per gallon,which contains triethanol amine along with various amounts of higherboiling compounds, is charged to an esterification kettle that isprovided with an agitator, with means for heating the kettle, and withmeans for collecting and condensing volatile products of the reaction.Then a mixture of fatty acids from tall oil is added to the kettle in anamount approximating 1.5 moles of fatty acids per mole of alkanolamines. A representative example of tall oil fatty acids comprises 8%conjugated linoleic acid, 36% nonconjugated linoleic acid, 50% oleicacid, and 6% stearic acid, all percentages by weight.

After the tall oil fatty acids and the triethanol amine still bottomsare placed in the kettle there is added eight volume percent of xylenebased on the total mixturer Then the kettle agitator is started andheating of the kettle is begun, the reaction temperature being thatwhich will cause refluxing of the xylene. Water of reaction is collectedin a trap as an azeotrope with xylene. The azeotrope is sent to aseparator from which the xylene is continuously returned to the reactionmixture. Esterification is complete when no more water is collected overhead in the azeotrope, or when the temperature of the liquid in theesterification kettle reaches about 380-390 F. When it is determinedthat the reaction has been completed, the liquid reaction mixture iscooled and then about 20 vol. percent of xylene and 30 vol. percent ofheavy aromatic naphtha, both percentages being based on the volume ofreaction mixture, are added as solvents. Thereafter, 8 vol. percent,based on the mixture, of tris- (nonylphenyl)phosphite is added to themixture. The resulting product is an antifoulant prepared in accordancewith this invention. The antifoulant has the following approximateoverall composition in percentage by volume:

Percent Triethanolamine ester 62.2

Xylene 14.0 Heavy aromatic naphtha 18.8 Tris-(nonylphenyl)phosphite 5.0

The tris(nonylphenyl)phosphite was obtained by the reaction of threemoles of commercial nonyl phenol with one mole of PCl Example 2 Theantifoulant of Example 1 was compared with other prior art materialsmarketed as antifoulants with respect to the effectiveness of thesematerials to reduce fouling in the 5-hour Erdco CRC Fuel Coker Testdescribed in the article of A. W. Frazier et al., published in the Oiland Gas Journal, May 3, 1965, vol. 63, No. 18, page 117. In one set oftests, the feedstock that was used was a heavy gas oil from avisbreaking operation, having a boiling range of about 450 to 750 F. Ina second set of tests the feedstock was a vacuum residuum. In a thirdset of tests the feedstock was a conventional feed entering a catalyticreformer. This feed had an initial boiling point of 160 F. and a finalboiling point of 325 F. In the first set of tests the amount of anti- 6foulant that was used was 40 parts by weight per million of feedstock;in a second set of tests the amount was 50 parts per million; and in thethird set of tests, the amount of antifoulant was 25 parts per millionof feedstock. Comparative tests were also run with each feedstockcontaining no added antifoulant.

In each case, a five-gallon sample of the untreated or treated feedstockwas used. When additive concentrates were used they were diluted with anequal volume of kerosene before addition to the feedstocks. Upon runningthe feedstocks through the apparatus shown in FIG. 1 of the articlereferred to, under the test conditions set forth in that article, andafter measuring the pressure drops across the porous filter, thepressure drop was plotted against the length of the test, in minutes,and the linear slope Was determined. By linear slope is meant the slopecalculated as if the approximately semilogarithmic plot of Frazier etal. were linear, i.e. a 45 line will have a slope of unity. The lowerthe slope, the less fouling occurred; the higher the slope, the morefouling occurred. Also, in some of the runs appearing in the followingTable I, the pressure drop in inches of mercury ("HgAP) across thefilter is given. A high fouling feed quickly reaches a 25-inch pressuredifferential while a low fouling feed more slowly reaches this samepressure differential.

TABLE I.FUEL COKER TEST RESULTS Coker test data Linear Hg AP at Min. to25 Additive slope 250 min, Hg AP 30 p.m. in heavy gas oil:

None .65 Amino ester alone a 0. 40 Polyamine amide 0. 50 Example 1product- 0.00

50 p.p.m. in vacuum residuum:

None Polyamine amide b Amide plus phosphite Amide plus amino phenol 4Example 1 product 25 ppm. in cat. reformer tee Amide plus phosphiteExample 1 product It is to be noted from the data in Table I that theadditive mixture of the present invention was superior to all of theother prior art antifoulants when used in each of the feedstocks thatwere tested.

It is to be understood that the specific embodiments herein presentedare by way of example and that the scope of the invention is not to belimited thereto. The scope of the invention is defined by the appendedclaims.

What is claimed is:

1. A method for treating an organic feedstock that is fed to a heatexchange step wherein it is subjected to a temperature in the range ofabout 200 F. to about 1300 F. which comprises adding to said feedstockfrom about 0.5 to about 200 parts per million, based on the weight ofthe feedstock, of a mixture of from about 75 to 99 wt. percent of a C toC fatty acid ester of an alkanolamine and from about 1 to about 25 wt.percent of a phosphite compound having the formula:

wherein R, R, and R" are hydrogen or a hydrocarbon radical selected fromthe group consisting of alkyl, halo- 7 alkyl, aryl, haloaryl, alkaryl,haloalkaryl, cycloalkyl, halocyclo alkyl, alkenyl, haloalkenyl, aralkyl,and haloaralkyl, whereby fouling of heat exchange equipment as theresult of oxidation or polymerization of feed stock constituents isreduced.

2. A method as defined by claim 1 wherein the amount of said mixture isbetween about 0.5 and 60 parts by weight per million of said feedstock.

3. Method as defined by claim 1 wherein said organic feedstock comprisesa normally liquid petroleum hydrocarbon fraction.

4. Method as defined by claim 1 wherein said fatty acid ester comprisesethanolamine esters of oleic acid or of mixed fatty acids includingoleic acid.

5. Method as defined by claim 1 wherein said fatty acid ester comprisesthe tall oil fatty acid esters of triethanol amine.

6. Method as defined by claim 1 wherein said fatty acid ester comprisesthe tall oil fatty acid esters of triethanol amine still bottoms.

7. Method as defined by claim 1 wherein said phosphite is an ester of aC to C alkyl phenol.

8. Method as defined by claim 1 wherein said phosphite comprisestris(nonylphenyl)phosphite.

9. An organic feedstock normally tending to form fouling deposits inheat exchange equipment when subjected to a temperature exceeding about200 E, which has been treated to reduce said fouling tendency byincorpowherein R, R, and R" are hydrogen or a hydrocarbon radicalselected from the group consisting of alkyl, haloalkyl, aryl, haloaryl,alkaryl, haloalkaryl, cycloalkyl, halocyclo alkyl, alkenyl, haloalkenyl,ar-alkyl, and haloaralkyl.

References Cited UNITED STATES PATENTS 2,889,389 11/1959 Fierce et a1.208348 3,218,137 11/1965 Belo et a1. 4466 3,364,130 1/1968 Barnum 20848AA DELBERT E. GANTZ, Primary Examiner G. E. SCHMITKO-NS, AssistantExaminer US. Cl. X.R.

